A circular knitting machine aims to knit fabrics of varying colors and patterns. It has a rotary circular disc with radial cams and actuators at the bottom and a plurality of color altering heads located below. Each color altering head has a plurality of yarn changing sets. During operation, each actuator selects one yarn changing set of the color altering head and the cam pushes a movable cutter plate and a yarn changing plate in the yarn changing set to move alternately to drive a yarn to a yarn feeding port to switch yarns of different colors.
Refer to FIGS. 1 and 2 for a conventional structure. It includes a color altering head 1 with a plurality of yarn changing sets 12 (four sets are shown in the drawings) located between two splint plates 11. Each yarn changing set 12 has a yarn changing plate 121, a yarn cutting plate 122, a movable cutter plate 123 and a yarn splint plate 124. The yarn cutting plate 122 and the yarn splint plate 124 have a plurality of holes 1221 and 1241 coupling with a plurality of pins 125. The movable cutter plate 123 and yarn changing plate 121 have respectively confining slots 1211 and 1231 in the center. The movable cutter plate 123 is movably interposed between the yarn cutting plate 122 and yarn splint plate 124. The yarn changing plate 121 is located outside the yarn cutting plate 122. The pins 125 in the center run through the confining slots 1211 and 1231. The pins 125 located on the periphery butt the edges of the movable cutter plate 123 and yarn changing plate 121 to confine moving direction of the movable cutter plate 123 and yarn changing plate 121 so that the movable cutter plate 123 and yarn changing plate 121 can be moved reciprocally to crochet and cut a yarn. The yarn cutting plate 122 also has another two confining slots 1222 at one side.
When the circular knitting machine operates for a time period, the reciprocal yarn movement generates cotton which gradually accumulates between the yarn cutting plate 122 and yarn splint plate 124, and also in the confining slots 1211 and 1231 of the yarn changing plate 121 and movable cutter plate 123. Operation becomes unsmooth. Even elements could be damaged. Hence a periodic repair and maintenance have to be performed after a period of time. Due to the color altering head 1 adopts a closed design, all elements have to be disassembled during repair and maintenance. This is time consuming and results in lengthy operation interruption. There are still rooms for improvement.